The present invention relates to a radio telephone system and a terminal therefor.
A mobile telephone system is an example of a radio telephone system which is currently available. In this telephone system, a plurality of telephone service companies offer services within a single area. A radio terminal, i.e., a mobile station, is registered in one of the companies, and the subscriber can get services only within the telephone network or system of this company. Therefore, the subscriber cannot arbitrarily select a telephone service company or a telephone system.
In a mobile telephone system, radio frequencies are assigned fixedly to respective radio base stations. For this reason, when a plurality of systems are to be installed in a single area, different frequencies are assigned to the respective systems, even if they operate according to the same control scheme. The systems can be classified as "public" or "private" radio telephone systems. Public systems are characterized by widespread availability throughout a geographic area, but private systems are generally available only within limited areas, such as a compound, office complex, factory, home, or the like.
On the other hand, demands have arisen for service diversification which allows each subscriber to arbitrarily select a system depending on differences in services and charges between wireless communication networks. That is, a common air interface needs to be used. The above-described systems, however, are not designed to use a common air interface.
In the second-generation cordless telephone plan, which has recently been proposed in Japan, the use of a common air interface has been considered. In this plan, one radio terminal can be used in the home and office, and outdoors. As disclosed in Japanese Patent Application No. 5-155518, in such a system, it is important that the radio connection can be made through the common radio terminal of a user even if the home and office are located in the service area of a radio connection unit installed by a different telephone service company.